In providing an optical communication system, an optical exchange system, etc, optical devices such as an optical modulator, an optical combining an branching device, an optical switch, an optical multiplexing and demultiplexing device etc. are generally used as based structural elements. These devices generally comprise optical waveguides. For this structure, it is inevitable to optically couple optical waveguides and optical fibers. The importance of the optical coupling between optical waveguides and optical fibers is enhanced under the situation where subscriber's networks have been increasingly changed to optical systems replacing electric systems, and optical devices have been more and more integrated into semiconductor substrates. In accordance with this tendency, the characteristics such as low loss of light, easy fabrication, stability against external force and heat are required for the optical devices.
Conventionally, an optical fiber and an optical waveguide are positioned to lower optical coupling loss to the minimum extent by using an optical jig, and fixed at the smallest coupling loss-position by using optical adhesive.
In this method of coupling the optical fiber to the optical waveguide, however, there are disadvantages in that
(1) the position adjustment takes a long time, PA1 (2) the optical coupling process is carried out one by one to lower the mass-productivity, and PA1 (3) the reliability is low against external force. PA1 a crystalline substrate having first and second regions; PA1 an optical waveguide formed on the first region of the crystalline substrate; PA1 a V-shaped groove formed on the second region of the crystalline substrate, the V-shaped groove being formed by anisotropic etching of the crystalline substrate; and PA1 an optical fiber placed in the V-shaped groove, a light axis of the optical fiber being aligned to a light axis of the optical waveguide to provide an optical coupling between the optical waveguide and the optical fiber; PA1 wherein the V-shaped groove comprises inclined planes defining a V-letter in cross-section, each of the inclined planes being intermittent to support the optical fiber at an interval.
In order to overcome the disadvantages, an optical coupling device for optically coupling an optical fiber to an optical waveguide has been proposed, for instance, as described on pages 391 to 395 of "Applied Optics, Vol. 13, No. 12, February 1974", on pages 166 and 167 of "Integrated Photonics Research, TuD 6-1 and TuD 6-2", and on page 4-315 of "the Spring session in the electron information and communication academic society, 1993".
The conventionally proposed optical coupling device comprises an optical waveguide having a core layer and a clad layer provided on a silicon substrate, and a V-groove formed on the silicon substrate to be aligned to the core layer of the optical waveguide.
In assembly, an optical fiber is positioned in the V-groove on the silicon substrate to be aligned to the core layer of the optical waveguide. In fabrication, a silicon substrate is anisotropically etched on a (100) plane, so that a V-groove having slant surface of (111) planes is formed on the silicon substrate.
In the conventional optical coupling device, however, there is a disadvantage in that the parallel relation of an opening of an etching mask to an crystalline axis of a silicon substrate is difficult to be precisely set up, because an orientation flat of the silicon substrate has an error of approximately .+-.1.degree.. Unless the parallel relation is precisely set up, a width of a V-groove obtained by the anisotropic etching is larger than a specified value to lower the position precision of an optical fiber inserted into the V-groove. The detail of the disadvantage will be explained later.